Based on our preliminary work and published data, we hypothesize that the newly identified Secretory Protein-I (SP-I) is not restricted to the parathyroid alone but is present in many endocrine glands. We propose to test this hypothesis by attempting to identify, isolate and characterize these secretory proteins from key endocrine glands. The overall goal is to study the distribution of SP-I-like substance (SP) in different tissues and to compare these proteins from different tissues in terms of their structure, intracellular localization and their secretion along with individual secretory products or hormones. Specifically, we will start by surveying the existence of SP in a number of endocrine, exocrine and other tissues. Tissues will be homogenized in various solutions. The extracts will be subjected to radioimmunoassay using our rabbit anti-bovine SP-I serum and our bovine SP-I as standards. For tissues that contain appreciable amount of SP, standard procedures will be employed to separate subcellular fractions. These fractions will be examined for SP-I content. Alternatively, immunocytochemical staining techniques will be used to examine the existence and the localization of SP in different tissues. Once the initial survey is done, tissues that contain SP will be stimulated by different secretogogues in either the perfusion or incubation system. The secretion of individual hormone or secretory product will be examined alongside with the secretion of SP. Despite the results, whether a cosecretion phenomenon is universal or not in those tissue that contain SP, we will try to isolate and characterize the protein from key endocrine glands. Structural analysis coupled with intracellular localization studies should yield some information as to why they are or are not cosecreted with the hormone in a given gland. The isolation and characterization of SP from different endocrine glands may present for the first time a common biochemical denominator for studying the secretory process in general. The result may lead to a further and likely a unified understanding of the secretory process of these glands. This will help us to understand the regulation of secretion and will help in contemplating treatment of many diseases or pathological disorders that are associated with secretory dysfunction of these endocrine glands.